Influence of Minor Sc Addition on Microstructure and Mechanical Properties of Extruded Al–7Zn–2Mg–1.5Cu–0.1Zr Alloy in T6 Heat Treatment

Abstract

The effects of minor Sc on microstructure and mechanical properties of Al–7Zn–2Mg–1.5Cu–0.1Zr alloy under different aging time were investigated by means of tensile test, scanning electron microscopy and transmission electron microscopy, respectively. The results show that the aging strengthening tendency of Al–7Zn–2Mg–1.5Cu–0.1Zr(–0.2Sc) alloys exhibits the similar feature. After T6 treatment, the maximum values of ultimate tensile strength and yield strength are 700 MPa and 602 MPa, respectively. The tensile fracture of Al–7Zn–2Mg–1.5Cu–0.1Zr(–0.2Sc) alloys exhibits a mixed ductile-brittle fracture. The results of TEM observation show that large amounts of GP zones and η′ phase distribute homogeneously inside the grains, and some rod-like precipitates distribute along grain boundaries in two alloys. Besides, there also exist lots of Al₃(Sc, Zr) phase in Al–7Zn–2Mg–1.5Cu–0.1Zr–0.2Sc alloy with different treated states. The grain refinement strengthening and precipitation strengthening play the dominant role in the strength increase of the Al–7Zn–2Mg–1.5Cu–0.1Zr–0.2Sc alloy.